The Synology Photos UI feels much more polished and it includes a mobile app. Synology Photos only has community mobile apps, which weren't well maintained. And last I checked Photoprism did not have multi-user support. Synology Photos feels much more like something I could get my partner and kids to adopt.
The downside is that Synology Photo's database schema and API are not officially documented, but you can find people who have documented them and since it's on a machine you own you have unlimited access to them, so it's still a big step up from Google Photos and Apple Photos which are chock full of restrictions - e.g. Apple Photos doesn't even have a web API.
The downside is that Synology Photo's database schema and API are not officially documented, but you can find people who have documented them and since it's on a machine you own you have unlimited access to them, so it's still a big step up from Google Photos and Apple Photos which are chock full of restrictions - e.g. Apple Photos doesn't even have a web API.